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          tiny: sh, rm - reduced command line interface to the Inferno

          tiny/sh [ -n ] [ -ccommand ] [ file ]

          tiny/rm [ file ...  ]

          The tiny commands are smaller, simpler versions of more
          capable but larger Inferno commands.  They are provided for
          use on devices where a certain level of functionality might
          be useful for configuration or maintenance (or development),
          but device constraints are such as to make the use of the
          normal, fleshier versions of the commands unattractive.  For
          example, the Dis object files are typically 5 times smaller
          (or better) than the mainstream alternatives.  They live in
          the directory /dis/tiny, but could be placed in the /dis of
          a small device (eg, via root(3))ยท

          Rm removes files and empty directories, subject to the per-
          mission rules given in rm(1). There are no options.

          Sh provides a simple user level interface (a shell) to the
          Inferno system.  (It was once the only Inferno shell.)  It
          reads input lines, identifies a command and arguments for
          that command, and arranges for execution of the correspond-
          ing Inferno module.  There are features that allow
          input/output redirection, creating pipelines, and performing
          tasks in background.  It is nevertheless a rudimentary shell
          designed for starting and debugging applications.  It is not
          intended to serve as a general-purpose programmable shell.

          If a file is named as a command line argument, that file is
          the source of input; otherwise, standard input is read.

          Options are:

          -n   Don't fork the namespace.  By default, sh forks the
               namespace, making subsequent namespace changes invisi-
               ble to the previous namespace group.

               Execute the single command rather than prompting to
               read commands from the standard input.

        Command line syntax
          Each line consists of one or more command pipelines each
          separated by either an ampersand (&) which indicates that

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          the pipeline should be run in background or a semi-colon
          (;). The semi-colon need not be provided for the last com-
          mand pipeline on a line.

          Command pipelines are not allowed to span lines.

          Each command pipeline consists of one or more commands sepa-
          rated by a vertical bar (|) character. The standard output
          of one command is made the standard input of the next com-
          mand to the right.

          Redirection of input/output to pipes takes precedence over
          redirection from/to files.

          In the limit case, a command pipeline consists of a single
          command with no pipes.

          A command consists of one or more fields. The first (left-
          most) field is the command field. It is used to determined
          the executable file to be loaded and run; see below. The
          remaining fields are parsed and become command line argu-
          ments that are passed to the module's init function as a
          list of strings.

          Any input following a # on a line is discarded as comment.

        Finding the module
          The command field is converted to the pathname of the Dis
          file of some module. That field can be either an absolute
          pathname, starting from /, or a relative pathname from the
          current directory.

          As a convenience, the user need not specify the .dis suffix
          to the filename. If missing, it will be added by the shell.

          If the load fails there is, in general, a second attempt to
          load the module by resolving the pathname relative to the
          /dis directory (or any directory bound to the /dis directory
          in the current namespace).

          There are two exceptions to this second attempt. The second
          load attempt is not performed if the command field provides
          an absolute pathname or a relative pathname starting with
          dot-slash (./).  Such explicit naming is taken to mean that
          the user will accept no substitutions.

          The shell requires that the Dis file implement a module with
          an interface equivalent to the `Command' module as specified
          in /module/sh.m (see command(2)). Otherwise, the named file
          will not load.

          In lieu of a path mechanism, a process can create a union

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          directory at /dis.

        File name expansion
          Command line arguments (including the command field itself)
          are expanded by the shell according to the regular expres-
          sion rules described in filepat(2).

          This expansion is not applied to the filenames used for
          input/output redirection.

          The shell special characters can be stripped of their mean-
          ing and treated as literals by enclosing them in single
          quotes. Inside a quoted string, the special meaning of the
          single quote can be removed by immediately following it with
          another single quote. Command lines with un-terminated
          quoted strings are rejected and cause an error message.

          For example:

               $ echo ''''
               $ echo 'don''t'
               $ echo 'hello' 'world
               sh: unmatched quote
               $ echo 'a'b
               $ echo a'b'

        Shell special characters
          The following characters are treated specially by sh and
          must be quoted to be taken literally:

               white space, except in a quoted string

          tab  white space, except in a quoted string

               command line terminator

          #    Start of comment

          '    Start of/end of quoted string (single quote)

          |    Interface between commands in a command pipeline.

          &    Terminator for command pipelines to be run in back-

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          ;    Terminator for command pipelines to be run syn-
               chronously by the shell.

          >    Output re-direction: create file if it does not exist;
               truncate file if it exists

          >>   Output re-direction: create file if it does not exist;
               append to file if it exists

          <    Input re-direction.

          The shell uses a prompt consisting of the system name as
          provided by /dev/sysname suffixed by $.

        Input/output re-directions
          By default, standard input is the console keyboard and stan-
          dard output the console display. Each command can specify
          that standard input be taken from a file and standard output
          be written to a file.

          Attempts to redirect standard input to a non-existing file
          will fail. Redirecting standard output to a non-existing
          file will cause that file to be created. If the destination
          file already exists, it will be overwritten. Any previous
          contents are lost.

          In cases of competing re-direction mechanisms (re-direct to
          a file and to a pipe), the pipe has precedence.

        Background tasks
          In general, the shell waits for the termination of a command
          pipeline before continuing execution, for example, prompting
          the user for the next command. However, if the command pipe-
          line is terminated by an ampersand (&) character, the wait
          stage is skipped and the shell continues execution immedi-
          ately, in this case the command pipeline executes as a back-
          ground task.

        Name space concerns
          When started, the shell creates an independent file name
          space that is a copy of the file name space of the shell's

          Command pipelines started by the shell are executed by
          threads that share the shell's name space. If those commands
          modify the file name space (and they have not mimicked the
          shell in creating their own independent name space), those
          modifications will be perceived by the shell when it contin-
          ues execution. See bind(1) and sys-pctl(2).


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          bind(1), sh(1), filepat(2), command(2), sys-pctl(2),
          cons(3), pipe(3), prog(3)